1. Field of the Invention
Embodiments of the present invention relate generally to a method, a system and various devices for sustained medical infusion of fluids, and more particularly, to a system having a portable infusion device (preferably miniature) adherable directly to a patient's skin, and to associated methods and devices for accurate dispensing of fluids from the device into the body of the patient. Some embodiments of the present invention relate to the connection of two or more separate portions (e.g., planar connection), such as a disposable portion and a reusable portion, preferably forming a flexible, pliable and thin skin-compliant device (e.g., patch).
2. Background of the Invention
Medical treatment of several illnesses requires continuous drug infusion into various body tissues, through subcutaneous and intra-venous injections (for example). Diabetes mellitus patients require the administration of varying amounts of insulin throughout the day to control blood glucose levels. In recent years, ambulatory portable insulin infusion pumps have emerged as a superior alternative to multiple daily injections of insulin. These pumps, which deliver insulin at a continuous basal rate as well as in bolus volumes, were developed to liberate patients from repeated self-administered injections, and allow them to maintain a near-normal daily routine. Both basal and bolus volumes must be delivered in precise doses, according to an individual prescription, since an overdose of insulin could be fatal. Therefore, insulin injection pumps must be highly reliable to prevent delivery of any unintentional excess insulin.
Several ambulatory insulin infusion devices are currently available on the market. Generally, these devices have two parts: a reusable portion, containing a dispenser, a controller and electronics, and a disposable portion containing a reservoir, a needle assembly, with cannula and trocar, and a fluid delivery tube. The insertion of a variety of needles of different length and insertion angles, as required by the location of the injection on the body, demands a great deal of skill and practice. Usually, the patient fills the reservoir, attaches the needle and the delivery tube to the exit port of the reservoir, and then inserts the reservoir into the pump housing. After purging air out of the reservoir, the tube and the needle, the patient inserts the needle assembly, trocar and cannula, at a selected location on the body, and withdraws the trocar. To avoid irritation and infection, the subcutaneous cannula must be replaced and discarded after two to three days, together with the empty reservoir.
Examples of first generation disposable syringe-type reservoir and tubes were described in 1972, by Hobbs, in U.S. Pat. No. 3,631,847, and in 1973, by Kaminski, in U.S. Pat. No. 3,771,694, and later by Stempfle, in U.S. Pat. No. 4,657,486, and by Skakoon, U.S. Pat. No. 4,544,369. The driving mechanism of these devices is a screw thread driven plunger controlling the programmed movement of a syringe piston. Other dispensing mechanisms have been described including peristaltic positive displacements pumps, for example in 1980, by Wilfried Schal et al, in U.S. Pat. No. 4,197,852, and later by Schneider, in U.S. Pat. No. 4,498,843, and by Wolff, in U.S. Pat. No. 4,715,786.
These devices represent a significant improvement over multiple daily injections, but all suffer from several drawbacks. The main drawback is the large size and the weight of the device, caused by the spatial configuration and the relatively large driving mechanism of the syringe and the piston. The relatively bulky device had to be carried in a patient's pocket or attached to a belt. Consequently, the fluid delivery tube is long, usually longer than 40 cm, to permit needle insertion in remote sites of the body. These uncomfortable bulky devices with a long tube are rejected by the majority of diabetic insulin users, since these devices disturb regular activities, such as sleeping and swimming for example. Furthermore, the effect of the image projected on a teenagers' body is unacceptable.
In addition, the delivery tube excludes some optional remote insertion sites, like the buttocks and the extremities. To avoid the tubing limitations, a second generation of such devices has been devised. These devices included a housing having a bottom surface adapted for contact with the patient's skin, a reservoir disposed within the housing, and an injection needle adapted for communication with the reservoir.
This paradigm was described by Schneider, in U.S. Pat. No. 4,498,843, Sage in U.S. Pat. No. 5,957,895, Connelly, in U.S. Pat. No. 6,589,229, and by Flaherty in U.S. Pat. Nos. 6,740,059 and 6,749,587, none of them being currently available on the market. The above-mentioned second-generation devices have several limitations. They are bulky, because the reusable dispensing portion including the driving mechanism, is assembled on top of the disposable needle/reservoir portion. Such a “sandwich shaped” design, and their stacking in at least two layers, leads to a relatively thick device having thickness of between 15 to 20 mm. Moreover, upon the needle emerging from the bottom of the device during insertion (either manually or automatically), the needle is usually inserted perpendicular to the skin (e.g., a predetermined angle) that for most patients is inconvenient and requires some skill to accomplish. The device was abandoned by patients wanting to see the puncture site and preferring needle insertion angles of less than 30°.
Second-generation devices with a positive displacement peristaltic dispenser, e.g. Flaherty in U.S. Pat. No. 6,749,587, are provided with the drive mechanism and engine contained within the reusable portion, which is positioned on top of the pumping wheel, contained within the disposable portion. This configuration exhibits major limitations that are associated with inefficient energy utilization, and constant, long term pressure of the pump's wheel(s) applied on a transfer tube during the entire shelf life of the dispenser. Due to long term pressure the operation of the dispenser might be associated with inaccuracies because of the creeping of plastic material, from which the transfer tube is made. Another disadvantage of the above-mentioned configuration is associated with the fact that it allows air purging only after assembling of all the parts of the dispenser and requires operating the engine.
Other drawbacks of second-generation devices include leaking connections between reusable and disposable portions, as well as unavailable water resistance. Finally, a major limitation for the widespread acceptance of first and second generation pumps is their extremely high purchase price, running from $4000 to $6000, and maintenance costs amounting to some $250 per year.
Thus, there is a need for a miniature portable programmable fluid dispenser having an insertion needle which does not require direct connection with a connecting tube, and that allows direct adhesion to the patient's skin at any desired location on the body, and that could be remotely controlled. Preferably, the disposable portion of the device should contain a reservoir allowing manual filling and purging of air. After connection of the reusable and the disposable portions, the thickness of the unified device should be small (e.g., less than five (5) mm). Furthermore, the reusable portion should contain a high precision peristaltic pump for very accurate dispensing doses of fluid.